Chemical bonding Flashcards
what is a kernel?
Kernel: is the nucleus and all inner electrons
Octet rule
An element attain stability by have 8 electrons in its valance shell by sharing or complete transfer of electron
Drawbacks:
1. Element having atomic number less that 4 have unfilled electrons
2. Elements having d orbital are having extended octet
3. Some elements are having odd number of electrons
Noble gases like Xe and Kr form bonds
What was Kossel-Lewis method of representation of atoms?
With the symbol of the element and showing its valence shell electron using dots
Drawbacks:
1. didn’t give the shape, nature and energy levels of compound and molecules
Formal charge
method used foe balancing and keeping track of electrons in the molecule
FC = V - L - B
V = valence electrons
L = Lone pair
B = number of bonds
What are the main feature that define an ionic bond?
The main feature that define an ionic bond are:
1. Electron gain enthalpy: the energy releases or absorbed when electron is gained
2. Lattice enthalpy: the energy required to break one mole of bond into gaseous ions
Why do we need bond parameters?
Bond parameters are parameters that help define a bond thus they are important.
How is bond enthalpy and lattice enthalpy different?
Bond enthalpy deals with the amount of energy required to break one mole bond present in gaseous state
where as lattice enthalpy is the energy require to break one mole of bond to give gaseous ions
How is bond length and bond order related ?
Bond length is the length between the nuclei of two atoms where as bond order is the number of bond that atom is forming
Bond length increases bond order decreases
Bond angle
The angle formed between any two bonds. Depends on the compound
Resonance
Canonical structure: the representation of the same molecule in multiple way. (need one single bond and one double bond)
Resonance: different canonical structure lead to a formation of a hydride where the energy is less and that compound is more stable
Why is the resonance hybrid more stable that their canonical structures ?
This is because the hybrid averages the bond character
What results in the formation of a polar bonds?
Polar bonds are formed due to difference in electronegativity, because of there is is a distortion of electrons towards the more electronegative atoms creating a partials charge
Dipole moment
Charge * distance of separation
it is a vector quantity
Fajan’s Rules
No compound is purely ionic or covalent, they have the properties of both
- larger anion and smaller the cation more covalent
- more charge on the cation more covalent
- more polarizing cation and more polarizability of anion more covalent
What was the main principle behind the VSEPR theory?
VSEPR theory
Valence shell electron pair repulsion theory
1. the positions acquired in 3-D lead to min repulsion
2. the shape of the compound depends the number of valance electrons
3.Valance shell is considered as a sphere
4.Electron pair repel each other
LP-LP>LP-BP>BP-BP
5. multiple bonds = single electron pair
multiple multiple bonds = super electron pair
What kind of geometry does these type of molecules have
1. AB2
2.AB3
3.AB4
4.AB5
6.AB6
- linear geometry with angle of 180
- trigonal planer with angle of 120
3.Tetrahedral with angle of 109.5 - trigonal bipyramidal angle of 90,120
- Octahedral with angle of 90,90
What kind of structure do these kind of molecules have:
1.Ab2E
2.AB3E
3.AB2E2
4.AB4E
5.AB3E2
6.AB5E
7.AB4E2
- bent shape with angle of 119.5
2.trigonal pyramid with angle of 107 - bent shape with angle 104.5
- Sew saw with angle 90,120
- t shaped with angle 90
6.Squar pyramid - Squar planner
Why are axial bonds longer that equatorial bonds?
Because axial bond face more repulsion rather that equatorial bonds
What is the principle of VBT?
Attraction and repulsion between two atoms and molecules
What are the result of these attractive and repulsive forces?
Due to these attractive and repulsive force there is overlapping of orbitals
What is overlapping ?
Overlapping means the merging of orbitals
more the over lapping more stronger is the bond
types of overlapping
1. positive overlapping: same signs overlapping
2. negative overlapping: different signs overlapping
3. Zero overlapping: on overlapping at all
What are the two types of bond formations?
- Sigma bond : a bond formed due to head on overlapping of orbitals. It is strong, independent and rotatable
- Pi bond: a bond formed due to lateral overlapping of orbitals. They are weak dependent and are not rotatable
What is hybridization?
The intermixing of atomic orbitals of similar or same energy to form a hybrid orbitals with equivalent energy and shape.
Feature of hybridization
- no. of HO = no of AO
- bonds formed are more stable
- need to similar energy levels
- The orbital need to be half filled
5.propotion of electron is not necessary
What are the different types of hybridisation?
- sp linear alkyne 50-50
2.sp2 trigonal planner alkene 33-67
3.sp3 tetrahedral alkane 25-75
4.sp2d squar planner
5.sp3d trigonal pyramid
6.sp3d2 squar pyramid
Feature of MOT
Molecular orbital theory
1. no of electrons in Mo = no of electrons is AO
2.similar energy level of AO form MO
3. Influenced by more that one nuclei i.e polycentric
4. types of orbital
a) bonding: less energy, more stable and hold the atoms together
b) anti-bonding: more energy, less stable creates a node between atoms
Overlapping should be done along the same axis and the overlapping need to be max.
Energy level diagram for MOT
- kk(σ2s)(σ2s)(σ2pz)(π2px=π2py)(π2px=π2py)(σ2pz) after nitrogen
- kk(σ2s)(σ2s)(π2px=π2py)(σ2pz)(π2px=π2py)(σ2pz) before nitrogen
How comes C2 form two pi bonds instead of one pi and one sigma?
This is because carbon need 4 electrons to be stable then the formation of two pi bond full fills that
Hydrogen bond
attractive forces between H and an electronegative element forming a weak bond.
the magnitude of the bond depends on the state in which the sub. is present
S>L>G
What are the different types of hydrogen bond
There are two different type of hydrogen bond:
1. inter molecule: with another molecule of the same or different compound
2. Intramolecular: within the same molecule between two electronegative elements
